Tears of the Subscapularis Tendon in Athletes
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Tears of the SubscapularisTendon in AthletesçDiagnosis and RepairTechniques a b, Dana P. Piasecki, MD , Gregory P. Nicholson, MD * KEYWORDS Subscapularis Repair Tendon Tears Diagnosis Isolated injury to the subscapularis tendon is an uncommon—but potentially debilitat- ing—injury among athletes. The most frequent injury pattern seen in younger athletes is an acute, traumatic tendon avulsion. In the older athletic population, chronic degen- erative tearing of the tendon may precede sports-related rupture, particularly after shoulder dislocation. This article reviews how to diagnose this injury in athletes and describes both conservative and operative treatment options and their outcomes. Although a growing body of literature has come to recognize isolated subscapularis tendon tears in a typically nonathletic population, little has been written on the analo- gous pathology in active, athletic patients. Injury to this portion of the rotator cuff, however, does occur, with clinical implications ranging from diminished athletic per- formance to serious disability. Familiarity with the potential injury patterns in an athletic population as well as an understanding of the diagnostic workup and appropriate treatment considerations are important to the practicing orthopedist. ANATOMY The subscapularis muscle–tendon unit comprises the anterior rotator cuff, providing active internal rotation of the humerus and contributing to the dynamic anterior stabil- ity of the glenohumeral joint. Nervous innervation is provided via the upper and lower subscapular nerves and their variable branches that enter the muscle belly medial to the conjoint tendon.1 The muscle belly originates on the medial two thirds of the scap- ular body, developing a tendinous character at the more lateral joint line and inserting at the lesser tuberosity in coalescence with the anterior shoulder capsule.2 At the joint a Division of Orthopaedic Sports Medicine, Midwest Orthopaedics at Rush, Rush University Medical Center, Suite 1063, 1725 West Harrison Street, Chicago, IL 60612, USA b Division of Orthopaedic Sports Medicine and Shoulder and Elbow Surgery, Midwest Orthopaedics at Rush, Rush University Medical Center, Suite 1063, 1725 West Harrison Street 1063, Chicago, IL 60612, USA * Corresponding author. E-mail address: [email protected] (G.P. Nicholson). Clin Sports Med 27 (2008) 731–745 doi:10.1016/j.csm.2008.06.005 sportsmed.theclinics.com 0278-5919/08/$ – see front matter ª 2008 Elsevier Inc. All rights reserved. Downloaded for Anonymous User (n/a) at Rush University from ClinicalKey.com by Elsevier on December 31, 2018. For personal use only. No other uses without permission. Copyright ©2018. Elsevier Inc. All rights reserved. 732 Piasecki & Nicholson line, subscapular and subcoracoid bursae lubricate the muscle–tendon’s articulation with the more posterior joint capsule and anterior coracoid process, respectively.3 The tendon has its greatest bulk superiorly, tapering off to a thinner, more muscular layer inferiorly.2 The dimensions of the bony insertion follow this theme, with a wider superior aspect (1.8–2.0 cm from medial to lateral) that thins toward the bottom of the lesser tuberosity (mean, 0.3 cm medial to lateral width), creating a trapezoidal inser- tion whose greatest dimension is its vertical lateral edge (2.5–4 cm from proximal to dis- tal).4–6 The tendon’s insertional fibers also extend posteriorly and laterally over the top of the bicipital groove, coalescing with insertional fibers of the supraspinatus—as well as the coracohumeral (CHL) and superior glenohumeral (SGHL) ligaments—to form the biceps pulley complex, performing an important stabilizing role for the biceps ten- don.7,8 Biomechanically, the superior and midportions of the tendon have substantially greater stiffness and ultimate load to failure than the tendon’s inferior portion, providing a measure of protection against propagation of cuff tears superiorly but theoretically posing a region of vulnerability to anterior shoulder dislocation inferiorly.9 PATHOPHYSIOLOGY Acute, high-energy sports-related events are the most commonly reported mechanism of subscapularis tears in athletes. Among sports as varied as waterskiing, baseball, and arm wrestling, several investigators have reported either partial or complete tendon rupture after a typically violent hyperextension or combined adduction and external rotation maneuver.10–12 In skeletally immature athletes, in whom the physes are generally weaker than musculotendinous or tendinous tissues, similar mechanisms may instead cause frank lesser tuberosity bony avulsions.13–17 In older athletes, the tendon usually ruptures first and with generally lower energy events. Particularly among athletes older than 40 years, the prevalence of pre-existing degenerative, partial-thick- ness articular-sided fraying18–20 may weaken the tendon at its insertion, increasing the likelihood of full-thickness rupture during less-violent sporting activities.21–23 Similar age-related differences are seen after shoulder dislocations, in which younger patients typically present with a Bankart lesion, whereas older athletes are much more likely to suffer full-thickness rotator cuff tears—particularly of the subscapularis.24 Chronic overuse-related microtrauma and tendon degeneration may play an impor- tant role in predisposing athletes to traumatic rupture, particularly in older age groups. Several investigators have hypothesized that the tendon may be chronically injured by a mechanical compression between the lesser tuberosity and coracoid process25–27—the so-called ‘‘roller wringer effect’’—of particular significance in high-demand overhead athletes.28 Another contributory mechanism of injury is ante- rosuperior impingement, in which articular-sided abrasion may occur at the lesser tuberosity and glenoid rim interface, especially in the resisted flexed and internally rotated positions (eg, the tennis follow-through).29,30 Such chronic, repetitive stress applied to the subscapularis musculotendinous junction could lead to microtrauma and eventually macroscopic tendon compromise.23,28,31 Whether sport-specific activ- ities predispose to such chronic overuse is not yet clear, although several studies have demonstrated tremendous subscapularis demands during certain sports. EMG analy- sis of golfers, for instance, suggests that the subscapularis dominates all other muscle activity during the golf swing, making it vulnerable to injury.32 Similar investigation has shown tremendous subscapularis demands during the tennis serve and forehand stroke,33 with a high frequency of ultrasound-confirmed subscapularis tendon calcifi- cations in the dominant shoulder of veteran (age, 35–77 years) tennis players.34 MRI of amateur baseball pitchers’ throwing shoulders has demonstrated significant increases Downloaded for Anonymous User (n/a) at Rush University from ClinicalKey.com by Elsevier on December 31, 2018. For personal use only. No other uses without permission. Copyright ©2018. Elsevier Inc. All rights reserved. Diagnosis and Repair Techniques 733 in subscapularis T2-weighted signal 48 hours after pitching,35 and an isolated subsca- pularis muscle strain has been reported in an outfielder.36 EMG study of swimmers has also suggested that the butterfly stroke places particularly high demands on the subscapularis muscle, with greater subscapularis activity associated with pain.37,38 Although these mechanisms would not appear to be the common primary mechanism of athletic subscapularis tendon tears—and have yet to be linked to increased rates of subscapularis pathology—they may well contribute to traumatic rupture when a suit- ably abnormal strain is applied. EPIDEMIOLOGY Isolated subscapularis tears in athletes are probably quite rare—particularly among young athletes—although the true incidence of these lesions is not currently known. The only published reports of these injuries in active patients younger than 40 years are small case series or case reports. Although the literature on older age groups is largely limited to degenerative tears, several studies suggest that sports-related tears are likely to be more common in older athletes. Although activity level was not spec- ified, Flury and colleagues39 reported isolated subscapularis tendon tears in 3% of their series of 1345 symptomatic rotator cuff repairs (mean age, 56 years) and Sakurai and colleagues18 noted a 13% rate of presumptively asymptomatic partial-thickness degenerative tears in their cadaveric study, suggesting that degenerative tears may occur with some frequency in these patients. Where reported, sports-related tears in older athletes tend to occur with less violence than in younger patients, and in as- sociation with degenerative tendons.21–23 Likewise, the association of these tears with shoulder dislocations24—as not infrequently occurs during contact sports—suggests that older patients may be expected to suffer sports-related subscapularis tears more frequently than their younger counterparts. DIAGNOSIS History A careful history should be obtained in all athletes presenting with shoulder pain and/or weakness. Specific to subscapularis injury, the time-course and mechanism of injury should be sought. Particularly in younger patients, subscapularis injury will typically follow a significant acute trauma in which the arm is forcibly hyperextended and/or externally rotated, although the diagnosis may be delayed.12,40 Older patients may re- port pre-existing mild pain in the anterior aspect of